Coil tubing injector for injecting tubings of various diameters

ABSTRACT

A multi coil tubing injector includes a frame structure and a pair of gripper chain drives mounted to the frame structure. The pair of gripper chain drives are disposed in a common plane and spaced apart from each other, and have gripping blocks adapted to engage one or more of at least three differently-sized coil tubing strings to inject the coil tubing strings into, or extract them from, a subterranean well. The coil tubing injector assembly reduces a time required to perform many downhole operations, and therefore reduces a cost of well completion, stimulation and re-completion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is the first application filed for the present invention.

MICROFICHE APPENDIX

Not Applicable.

TECHNICAL FIELD

The present invention relates generally to equipment for performingdownhole operations in subterranean wells. More specifically, theinvention relates to injectors for injecting coil tubing strings ofvarious diameters into subterranean wells and for extracting the coiltubing strings from the subterranean wells to perform well-servicingoperations.

BACKGROUND OF THE INVENTION

Continuous reeled tubing, generally known in the energy industry as coiltubing string, has been used for many years. It is rapidly gaining broadacceptance because is much faster to run into and out of a well casingthan conventional jointed tubing.

Typically, the coil tubing string is inserted into the wellhead througha lubricator assembly or stuffing box because there is a pressuredifferential between an annulus of the well and atmosphere, which mayhave been naturally or artificially created. The pressure differentialserves to produce oil or gas, or a mixture thereof from the pressurizedwell. A coil tubing string is run in and out of a well bore using a coiltubing string injector, which literally forces the coil tubing stringinto the well through the lubricator assembly or stuffing box againstthe well pressure until the weight of the coil tubing string exceeds theforce of the pressure acting against a cross-sectional area of the coiltubing string. However, once the weight of the coil tubing stringoverbears the well pressure, it must be supported by the injector. Theinjection process is reversed as the coil tubing string is removed fromthe well.

The coil tubing string is relatively flexible and can therefore be woundonto and pulled off of a spool, or reel, by the injector, which oftenacts in concert with a windlass at a power supply that drives the spool,or reel. Conventionally, a coil tubing injector assembly utilizes a pairof opposed endless drive chains which are arranged in a common plane.These opposed endless drive chains are often referred to as gripperchains and carry a series of gripping blocks that are pressed againstopposite sides of the coil tubing string, and thereby grip the coiltubing string. Each chain is stretched between a drive sprocket and anidle sprocket. At least one of the two drive sprockets is driven by amotor to turn one of the endless chains, to supply injection, retentionor lifting force. The other drive sprocket may also be driven, typicallyby a second motor, to drive the second chain in order to provide extrapower. Such coil tubing string injectors with various improvements aredisclosed, for example, in U.S. Pat. No. 4,655,291, entitled INJECTORFOR COUPLED PIPE, which issued to Cox on Apr. 7, 1987; U.S. Pat. No.5,553,668, entitled TWIN CARRIAGE TUBING INJECTOR APPARATUS, whichissued to Council et al. on Sep. 10, 1996; and U.S. Pat. No. 6,059,029,entitled COILED TUBING INJECTOR, which issued to Goode on May 9, 2000.

Another type of coil tubing string injector is disclosed in U.S. Pat.No. 5,566,764, entitled IMPROVED COIL TUBING INJECTOR UNIT which issuedto Elliston on Oct. 22, 1996. Elliston describes a coil tubing stringinjector unit including a main injector frame having a longitudinalopening that defines a vertical run for the injector unit, which can bealigned with the well bore's vertical axis. Elliston's injector unit hasonly one gripper chain drive system that carries plier-like halves thatare pivotable between an open position and a closed, gripping positionas the gripper chain enters the vertical run, so that the plier halvesgrip a selected length of a coil tubing string fed into the maininjector frame along the central vertical axis of the injector unit toinject the coil tubing string into the well bore.

U.S. Pat. No. 4,474,236, entitled METHOD AND APPARATUS FOR REMOTEINSTALLATION OF DUAL TUBING STRINGS IN A SUBSEA WELL, which issued toKellett on Oct. 2, 1984, discloses a method and apparatus for completinga well having production and service strings of different sizes. Themethod includes steps of running the production tubing string on a maintubing string hanger and maintaining control with a variable boreblowout preventer, and then running the service string into the maintubing string hanger while maintaining control using a dual bore blowoutpreventer.

Injector assemblies that are capable of injecting dual tubing stringsare also known in the prior art. The Applicant's U.S. Pat. No. 6,516,891(Dallas), which issued on Feb. 11, 2003, discloses a coil tubinginjector assembly that is capable of injecting dual string coil tubinginto a well bore simultaneously, either synchronously or asynchronously.

Although the Applicant has invented an apparatus for injecting andextracting two tubing strings, there does not exist, to the best of theApplicant's knowledge, any apparatus or method for the injection andextraction of tubing strings of several different diameters.

As is understood by those skilled in the art, coil tubing is availablein a variety of sizes and the size of tubing used for production, welltreatment or other special purpose depends on factors that are notalways known in advance. It is also common knowledge that the size ofcoil tubing installed in a well bore or to be installed in the well boreis not invariable correctly communicated to the service providerresponsible for injection or extraction of the coil tubing.

As a consequence, services providers must stack a plurality of coil tobe injectors which require a considerable capital investments and anextensive parts inventor for maintenance. In addition, if the wronginjector is delivered to a job site, costly delays are incurred whilethe appropriate injector is being delivered. Such delays increase thecost of hydrocarbon production and are desirably avoided.

Thus, there exists a need for a method and apparatus for injecting andextracting tubing strings of various diameters into or from asubterranean well.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a coil tubinginjector that can be used to selectively inject any of one or more of aplurality of differently-sized coil tubing strings into a well bore, orto extract the one or more coil tubing strings from the well bore.

The invention therefore provides a coil tubing injector assemblyincluding a frame structure for mounting above a wellhead; and at leastone gripper chain drive system mounted to the frame structure and havinga plurality of opposed gripping blocks adapted to grip any one of atleast three differently-sized coil tubing strings for injecting andextracting the coil tubing strings into and from a subterranean well.

The invention further provides a method of injecting or extracting oneof at least three differently-sized coil tubing strings into or from asubterranean well using a single coil tubing injector, including thesteps of gripping one of the at least three differently-sized coiltubing strings with one of at least three differently-sized grippingsurfaces formed on gripping blocks attached to opposed gripper chains;and driving the opposed gripper chains at substantially the same angularvelocity in opposite rotational directions to inject or extract one ofthe at least three coil tubing strings into or from the well.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will becomeapparent from the following detailed description, taken in combinationwith the appended drawings, in which:

FIG. 1 is a schematic side elevation view of a coil tubing injectorassembly mounted to a wellhead of a subterranean well in accordance withone embodiment of the invention, the injector assembly being capable ofinjecting and extracting into and from the well any one or more of fourcoil tubing strings of various diameters;

FIG. 2 is a schematic front elevation view of a first embodiment of theinvention in which a single gripper chain drive system is used to injectand extract any one or more of four differently-sized coil tubingstrings;

FIG. 3 is a schematic front elevation view of a second embodiment of theinvention, in which four independent gripper chain drive systems areused to inject and extract any one or more of four differently-sizedcoil tubing strings;

FIG. 4 is a side elevation view of a gripper chain drive system;

FIG. 5 is a cross-sectional view of a pair of gripping blocks, or“skates”, for use in the first embodiment of the coil tubing injectorassembly shown in FIG. 2;

FIG. 5 a is a cross-sectional view of four pairs of gripping blocks, or“skates”, for use in the second embodiment of the coil tubing injectorassembly shown in FIG. 3;

FIG. 6 is a cross-sectional view of a pair of gripping blocks, or“skates”, for use in injecting and extracting any one of fivedifferently-sized coil tubing strings;

FIG. 6 a is a cross-sectional view of five pairs of gripping blocks, or“skates”, for use in injecting and extracting any one of fivedifferently-sized coil tubing strings;

FIG. 7 is a cross-sectional view of a pair of gripping blocks, orskates, for use in injecting and extracting any one of threedifferently-sized coil tubing strings;

FIG. 7 a is a cross-sectional view of three pairs of gripping blocks, orskates, for use in injecting and extracting any one of threedifferently-sized coil tubing strings;

FIG. 8 is a cross-sectional view of a common drive shaft for drivingfour gripper chain drives;

FIG. 9 is a cross-sectional view of four independent drive shafts forindependently driving four gripper chain drives; and

FIG. 10 is a schematic cross-sectional diagram illustrating a method ofusing the multi coil tubing injector to inject four coil tubing stringsinto a well, either sequentially, as pairs, or all together where onecoil tubing string at each production zone is used for delivery of awell treatment fluid, such as a surfactant, while the other is used forthe production of hydrocarbon.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 and 2 schematically illustrate a coil tubing injector assemblyin accordance with the present invention, generally indicated byreference numeral 10. The coil tubing injector is positioned above awellhead 12, and may be supported by the wellhead 12, or on a groundsurface 14, in a manner well known in the art. A lubricator or stuffingbox 16 is connected to a top end of the wellhead 12 to contain wellpressure while coil tubing and/or downhole tools is/are run into or outof the well, as will be explained below in more detail.

The coil tubing injector 10 may be used to inject any one or more offour differently-sized coil tubing strings into a well. A first coiltubing string 17 is supplied from a reel 19. A second coil tubing string18 is supplied from a second reel 20. A third coil tubing string 21 issupplied from a third reel 23. A fourth coil tubing string 22 issupplied from a fourth reel 24. Each of the coil tubing strings has adifferent diameter, as illustrated. Although each coil tubing string isusually injected or extracted one at a time, it is also possible tosynchronously or asynchronously inject or extract two or more coiltubing strings. As noted above, dual injection of coil tubing strings isdisclosed in Applicant's U.S. Pat. No. 6,516,891 which issued on Feb.11, 2003 and is hereby incorporated by reference.

Each of the coil tubing strings is typically several thousand feet inlength. The four coil tubing strings 17, 18, 21, 22 are in a coiledstate as they are supplied from their respective reels 19, 20, 23, 24.The coil tubing strings are spooled from their respective reels, whichare normally supported on trucks (not shown) to provide mobility.

The coil tubing injector assembly 10 includes a frame structure 26,which may be constructed in any number of ways well known in the art.Extending upwardly from the frame structure 26 is a coil tubing guideframework 28 (shown in FIG. 1) that supports a plurality of rotatablymounted guide rollers 30 and 32 that guide the respective coil tubings17, 18, 21, 22 into the tubing injector. The coil tubing strings are runbetween respective sets of rollers 30 and 32, as better seen in FIG. 2.As the coil tubing strings are unspooled from their respective reels,their length is generally measured by respective measuring devices, suchas measuring wheels 33, 34, 35, 36 or the like. Alternatively, one ormore measuring device(s) may be incorporated into the coil tubinginjector assembly 10, in a manner well known in the art.

The rollers 30 and 32, which are supported by the framework 28, definefour pathways for each of the four coil tubing strings 17, 18, 21, 22 sothat any curvature in the coil tubing strings coming off the reels 19,20, 23, 24 is slowly straightened as the coil tubing strings enter thecoil tubing injector assembly 10. The respective sets of rollers 30 and32 are spaced apart so that straightening of the coil tubing isaccomplished as the coil tubing strings are inserted into the well by agripper chain drive system 37 which has a pair of substantiallyidentical gripper chain drives 38 spaced apart from one another anddisposed opposite each other in a common plane. The coil tubing strings17, 18, 21, 22 pass through the coil tubing injector assembly 10 and aresecurely supported in the grip of the pair of spaced gripper chaindrives 38, which include gripper blocks that are forced against each ofthe coil tubing strings 17, 18, 21, 22 to frictionally engage therespective coil tubing strings. The gripper chain drives 38 are drivenby means of pressurized hydraulic fluid, for example, in a direction tomove the coil tubing strings into or out of the well, as required.Pressurized hydraulic fluid may also be used to power a pressuremechanism for gripping or releasing the coil tubing strings as will beexplained below in further detail.

FIG. 2 is a front elevation view of the coil tubing injector assembly 10in accordance with the first embodiment of the invention. The coiltubing guide framework 28 includes adjacent coil tubing guides 29 a, 29b, 29 c, 29 d which are preferably interconnected by the coil tubingguide framework 28, though interconnection of coil tubing guides 29 a,29 b, 29 c, 29 d is not required. The coil tubing guide 29 a straightenscoil tubing 17 as it is fed between the gripper chain drives 38 of thegripper chain drive system 37. The coil tubing guide 29 b straightenscoil tubing 18 in the same way. Likewise, coil tubing guides 29 c and 29d straighten coil tubing strings 21 and 22, respectively. The multi coiltubing injector assembly 10 uses a plurality of, substantially identicalgripping blocks, each having multiple gripping surfaces, as will beexplained below in greater detail.

As depicted in FIG. 3, a second embodiment of the multi coil tubinginjector assembly 10 a has four gripper chain drive systems 37 a, 37 b,37 c, 37 d, each of which includes a pair of opposed, substantiallyidentical gripper chain drives 38. Each of the four gripper chain drivesystems is independently operable. The multi coil tubing injector 10 auses differently-sized gripping blocks, each having a single grippingsurface, as will also be described below in more detail.

FIG. 4 is a side elevation view of the gripper chain drive system 37.The gripper chain drive system 37 has two opposed gripper chain drives38 which are spaced apart to accommodate a length of tubing stringbetween the gripper chain drives 38. By rotating in opposite directions,the opposed gripper chain drives 38 cooperate to grip tubing strings andto inject or extract the tubing strings from a well. In FIG. 4, only thefirst coil tubing string 17 is visible (because the smaller diametertubing strings 18, 21, 22 are obstructed from view behind the first coiltubing string 17).

Each gripper chain drive system 37 is driven by a hydraulic motor 52preferably connected to a transmission which ensures that each opposedpair of gripper chain drives 38 moves at the same rate but in oppositedirections. As shown in FIG. 4, each gripper chain drive 38 includes agripper chain 42 which is driven by the drive sprocket 44 mounted to adrive shaft 46. The drive sprocket 44 and drive shaft 46 are connectedto hydraulic motors 52 through transmissions (not shown). An idlesprocket 48 is mounted to an idle shaft 50 and engages the lower loop ofthe gripper chain 42. The pair of drive shafts 46 are rotatably mountedto the frame structure 26 (FIG. 1). The idle shafts 50 are pivotallymounted to the frame structure 26 by means of a tensioner to provideadjustment of the tension of the gripper chains 42, using any one ofseveral tensioning systems well known in the art.

As shown in FIG. 4, inside each of the gripper chains 42 is a rollerchain 84. The roller chain 84 is built up from rollers connectedtogether by links and pins, in a well-known manner. The roller chain 84rolls freely about a periphery of a pressure beam 86 and is supported bya pair of sprockets 88 and 90, which are rotatably connected to thepressure beam 86.

The pressure beams 86 are movable toward and away from each other. Whenthe pressure beams 86 are moved toward each other, each pressure beam 86exerts a force against its roller chain 84 and the roller chain 84 bearsagainst the gripper chain 42 to force it against the coil tubing strings17, 18, 21, 22. Thus, when the pressure beams 86 are forced inwardlytoward each other, the coil tubing strings 17, 18, 21, 22 are grippedbetween the gripper chains 42. The gripping force is dependent upon theforce with which the pressure beams 86 are pressed against the rollerchain 84 by the actuators 92, which may be hydraulic cylinders, forexample. The pressure beams 86 are provided with trunnions 94, the endsof which are slidable within slots in the frame structures (not shown)so that the pressure beams 86 are supported by the frame structures andmovable with respect to the frame structure. The trunnions 94 areconnected to the respective actuators 92 which are also supported by theframe structure (not shown) so that the pressure beams 86 are controlledto exert the gripping force.

In a first embodiment of the invention, there is only a single gripperchain drive system for each gripper chain 42, and a plurality ofsubstantially identical gripping blocks 62 on each opposed gripper chain42. In another embodiment, each gripper chin drive system 38 has aplurality of gripping blocks 62 that are different from the grippingblocks 62 of the other gripper chain drive systems of the coil tubinginjector 10.

As shown in FIG. 4, each of the gripper chains 42 includes a pluralityof links 66 that interconnect the coil tubing gripping blocks 62. Eachgripping block 62, has a size and shape adapted to grip a least one coiltubing string. Each of the coil tubing gripping blocks 62 includes apair of pins 64 that connect the links 66 to the coil tubing stringgripping block 62 and engage teeth of the sprockets 46, 48. The adjacentcoil tubing string gripping blocks 62 are interconnected by link members66 to form an endless chain loop as shown in FIG. 4. In order to gripone of the coil tubing strings, each gripping block 62 has at least onegripping surface.

Illustrated in FIG. 5 is a pair of opposed gripping blocks 62 thatcooperate to inject and extract any one of four coil tubing strings,each having a different diameter. The gripping block 62 has a firstgripping surface 78, a second gripping surface 79, a third grippingsurface 80 and a fourth gripping surface 81 which are shaped to grip,respectively, the first tubing string 17, the second tubing string 18,the third tubing string 21 and the fourth tubing string 22. Asillustrated in FIG. 5, the four gripping surfaces 78, 79, 80, 81 haverounded contours and are sized to accommodate any one of fourstandard-size tubing strings each having a different diameter. Thegripping surfaces may be coated with a non-slip material to increase thecoefficient of static friction.

FIG. 5 a illustrates four differently-sized pairs of gripping blocks foruse with the second embodiment introduced with reference to FIG. 3. Inthis second embodiment, each of the four gripper chain drive systems 37a, 37 b, 37 c, 37 d has it own set of substantially identical grippingblocks 62 a, 62 b, 62 c, 62 d. The four gripping blocks 62 a, 62 b, 62c, 62 d have contoured gripping surfaces 78, 79, 80, 81 for gripping thefour coil tubing strings 17, 18, 21, 22, respectively.

In a further embodiment, the coil tubing injector 10 has a plurality ofsubstantially identical gripping blocks 62 that are capable of grippingany one of five coil tubing strings. In this embodiment, the coil tubinginjector has a single gripper chain drive system for injection andextraction of the coil tubing strings.

FIG. 6 shows an opposed pair of gripping blocks 62 having five grippingsurfaces sized and shaped to grip any one of five tubing strings havingdifferent diameters. Each gripping block 62 has five contoured grippingsurfaces 78, 79, 80, 81 and 82 which are capable of gripping any one offive coil tubing strings 17, 18, 21, 22, 25.

In yet another embodiment of the invention, the coil tubing injector hasfive independent gripper chain drive systems. Each gripper chain drivesystem has it own set of substantially identical gripping blocksarranged in opposed pairs. Any one of five coil tubing strings cantherefore be injected or extracted by driving the corresponding gripperchain drive system.

FIG. 6 a illustrates five differently-sized pairs of opposed grippingblocks 62 a, 62 b, 62 c, 62 d, 62 e which are mounted to five respectivegripper chain drive systems (not shown). The five sets of grippingblocks can be used to inject or extract any one or more of fivedifferently-sized coil tubing strings 17, 18, 21, 22, 25 into or from awell, either synchronously or asynchronously.

In another embodiment, the coil tubing injector has a single gripperchain drive system capable of injecting or extracting any one or more ofthree coil tubing strings. The gripper chain drive system employs aplurality of opposed gripping blocks having three gripping surfaces.

As illustrated in FIG. 7, each gripping block 62 has threedifferently-sized, contoured gripping surfaces 78, 79, 80 which arecapable of gripping three coil tubing strings 17, 18, 21 of differentdiameter. When the gripper chain drive system is driven, any one or moreof three coil tubing strings can be injected into or extracted from thewell.

In a further embodiment, the coil tubing injector has three independentgripper chain drive systems for injecting or extracting of any one ormore of three differently-sized coil tubing strings. Each of the threegripper chain drive systems has its own differently-sized set ofgripping blocks.

As shown in FIG. 7 a, the gripping blocks 62 a, 62 b, 62 c have grippingsurfaces 78, 79, 80, respectively, for gripping any one of three coiltubing strings 17, 18, 21. When one or more coil tubing strings are tobe injected or extracted, the gripper chain drive system(s) is drivenindependently of other two gripper chain drive systems that are not inuse.

Persons skilled in the art will appreciate that the coil tubing injectorin accordance with the present invention could be designed andconstructed to handle more than five tubing strings at a time. Thenumber of coil tubing strings that may be inserted or extracted isdependent on the number of gripping surfaces on the gripping blocks 62.

In a further embodiment, the differently-sized sets of gripping blocksthat were illustrated in FIG. 5 a, 6 a and 7 a (which have only onegripping surface), may be mounted to a common drive shaft such as shownin FIG. 8. Recalling, with regard to FIG. 4, that two opposed gripperchain drives constitute a gripper chain drive system, the mechanismshown in FIG. 8 therefore represents only one of the two sides of thegripper chain drive system. As noted above, in order to inject orextract a coil tubing string, two opposed common drive shafts mustrotate with substantially the same angular velocity but in oppositerotational directions. Therefore, the common drive shafts may be drivenby separate motors or by a common motor having suitable gearing torotate the opposed drive shafts at the same angular velocity but inopposite rotational directions.

As shown in FIG. 8, a common drive shaft 46 has four drive sprockets 44that are secured to the common drive shaft by respective keys 45. Thecommon drive shaft 46 is supported at one end by a bearing 47, such as aroller bearing, which is secured in a bore in the frame structure 26. Atransmission output sprocket 49, which may also be a gear, is alsoconnected by a key 45 (or a spline) to the drive shaft 46. Thetransmission output sprocket 49 is connected via a transmission (notshown) to the hydraulic motor 52. The hydraulic motor turns the driveshaft 46 about axis x by exerting a torque T_(x) on the drive shaft viathe transmission and transmission output sprocket.

In operation, the four drive sprockets 44 engage respective gripperchains 42 for injecting any one or more of four differently-sized coiltubing strings into or extending them from the well. Although FIG. 8shows four drive sprockets, persons skilled in the art will appreciatethat the common drive shaft could accommodate a different number ofdrive sprockets, such as three or five.

FIG. 9 shows a drive mechanism for a coil tubing injector in accordancewith the invention having four gripper chain drive systems, such as theone shown in FIG. 3. Each of the four gripper chain drive systems has apair of opposed gripper chain drives. Each pair of gripper chain driveshas one of four differently-sized sets of gripping blocks 62, such asthose illustrated in FIG. 5 a, for injecting or extracting one or moreof four coil tubing strings. Each gripper chain is driven via a separatedrive sprocket 44 a-44 d.

As shown in FIG. 9, the four drive sprockets 44 a-44 d (which driverespective gripper chains that are not shown) are mounted on fourindependent drive shafts 46 a-46 d. The drive sprockets 44 a-44 d aremounted to respective drive shafts 46 a-46 d by means of keys 45 so thatthe drive sprockets are rotated together with the drive shafts. Fourtransmission output sprockets 49 a-49 d are connected by keys 45 totheir respective drive shafts 46 a-46 d. Each transmission outputsprocket 49 a-49 d may be driven by an independent hydraulic motor andtransmission. Alternatively, one motor may be used to drive more thanone of the transmission output sprockets by suitable gearing permitstorque to be delivered to more than one output sprocket. As shown inFIG. 9, each of the four drive shafts 46 a-46 d run on a pair of rollerbearings 47, which are secured at opposite ends of each drive shaft 46a-46 d in bores in the frame structure 26 (FIG. 1). The fourindependently drivable shafts 46 a-46 d permit the synchronous orasynchronous injection or extraction of any one or more of fourdifferently-sized coil tubing strings.

In summary, the coil tubing injector in accordance with the inventionenables a user to inject or extract one or more of a number ofdifferently-sized coil tubing strings. Consequently, only one or moretubing injectors have to be kept in stack and the probability that anappropriate coil tubing injector is delivered to a job site is greatlyimproved. The coil tubing injector therefore significantly reducesoverhead, minimizes rig downtime and helps control the overall cost ofhydrocarbon extraction.

FIG. 10 illustrates one of many possible applications of the coil tubinginjector in which four differently-sized coil tubing injectors areinjected sequentially or together using the synchronous or asynchronousinjectors described above. The first and second coil tubing strings 17,18 are injected into the vicinity of a first production zone 100. Thethird and fourth coil tubing strings 21, 22 are injected into thevicinity of a second production zone 200. A plug or packer 150 istypically inserted between the first and second production zones toensure pressure isolation in a manner well known in the art. The firstcoil tubing string 17 is used to inject a well treatment fluid, such asa surfactant, into the first production zone 100 while the second coiltubing string 18 is used for production of hydrocarbons from the firstproduction zone. Likewise, the third coil tubing string 21 is used toinject a well treatment fluid into the second production zone 200, whilethe fourth coil tubing string 22 is used for production from the secondproduction zone.

Persons skilled in the art will readily appreciate that the coil tubinginjector in accordance with the present invention is adapted tofacilitate and expedite many other types of downhole operations in whichtime is saved by sequentially or synchronously injecting and/orextracting any one of a number of coil tubing strings using the sameinjector. The application shown in FIG. 10 is therefore intended to beexemplary only. It should also be understood that although the inventionhas been described with reference to coil tubing injectors for injectinga plurality of coil tubing strings of different diameters, two or moreof the gripping surfaces of each gripping block 62 could be sized togrip the same size of tubing.

The embodiments of the invention and the uses of the invention describedare illustrative but not comprehensive of the configurations and uses towhich the invention is adapted. The scope of the invention is thereforeintended to be limited solely by the scope of the appended claims.

1. A coil tubing injector assembly comprising: a frame structure formounting above a wellhead; and at least one gripper chain drive systemmounted to the frame structure and having a plurality of opposedgripping blocks adapted to grip at least one of at least threedifferently-sized coil tubing strings for injecting the coil tubingstrings into and extracting the coil tubing strings from a subterraneanwell.
 2. The assembly as claimed in claim 1 wherein each gripping blockcomprises at least one gripping surface adapted to grip one of theplurality of coil tubing strings.
 3. The assembly as claimed in claim 2wherein the gripping surface is concave.
 4. The assembly as claimed inclaim 3 comprising a single gripper chain drive system having a pair ofopposed gripper chain drives, each gripper chain drive including aplurality of substantially identical gripping blocks.
 5. The assembly asclaimed in claim 4 wherein the gripping blocks have at least threegripping surfaces.
 6. The assembly as claimed in claim 5 wherein eachgripping block has three differently-sized gripping surfaces forgripping at least one of three differently sized coil tubing strings. 7.The assembly as claimed in claim 5 wherein each gripping block has fourdifferently-sized gripping surfaces for gripping at least one of fourdifferently-sized coil tubing strings.
 8. The assembly as claimed inclaim 5 wherein each gripping block has five differently-sized grippingsurfaces for gripping at least one of five differently-sized coil tubingstrings.
 9. The assembly as claimed in claim 3 comprising at least threeindependently drivable gripper chain drive systems, each gripper chaindrive system having a pair of opposed gripper chain drives, each gripperchain drive system having a plurality of substantially identicalgripping blocks.
 10. The assembly as claimed in claim 9 wherein eachgripping block has a single gripping surface.
 11. The assembly asclaimed in claim 10 comprising three gripper chain drive systems eachhaving a differently-sized gripping surface.
 12. The assembly as claimedin claim 10 comprising four gripper chain drive systems each having adifferently-sized gripping surfaces.
 13. The assembly as claimed inclaim 10 comprising five gripper chain drive systems each having adifferently-sized gripping surface.
 14. The assembly as claimed in claim1 wherein the at least one gripper chain drive system comprises a pairof opposed gripper chain drives, each gripper chain drive having a drivesprocket mounted to a drive shaft, each drive shaft being coupled to amotor whereby the drive shafts of the opposed gripper chain drives arerotated at a same angular velocity but in opposite rotationaldirections.
 15. The assembly as claimed in claim 14 wherein each gripperchain drive further comprises: an idle sprocket mounted to an idleshaft; and a gripper chain engaged with the drive sprocket and the idlesprocket, the gripper chain having the gripping blocks attached aroundan outer periphery of the gripper chain.
 16. The assembly as claimed inclaim 15 wherein each gripper chain drive further comprises a pressurebeam supported by the frame structure and movable with respect to theframe structure, the pressure beam being adapted to support the gripperchains while the gripper chains grip the coil tubing string.
 17. Theassembly as claimed in claim 16 further comprising a roller chain systemoperatively mounted to the pressure beam for reducing friction betweenthe pressure beam and the gripper chain.
 18. The assembly as claimed inclaim 17 wherein the pressure beam is connected to an actuator mountedto the frame structure for moving the pressure beam.
 19. A method ofinjecting or extracting one of at least three differently-sized coiltubing strings into or from a subterranean well using a single coiltubing injector, comprising the steps of: gripping at least one of theat least three differently-sized coil tubing strings with at least oneof at least three differently-sized gripping surfaces formed on grippingblocks attached to opposed gripper chains; and driving the opposedgripper chains at substantially the same angular velocity in oppositerotational directions to inject or extract the at least one of the atleast three coil tubing strings into or from the well.
 20. The method asclaimed in claim 19 further comprising a step of actuating pressurebeams to force the gripping surfaces of the gripper chains against theat least one of the at least three coil tubing strings.